its a set damage amount because my low health stealthy mage assassin was instantly killed but my orc berserker with nothing but health and stamina walked away with over half his health. i forgot the levels of my characters so i dont know of the traps increase damage with your level or not. one of the first things im changing on my ever growing list is to make most traps insta kill. its especially weird getting hit by a huge swining axe and only losing a little bit of health. now sure why they made that design decision.
also i deliberately removed the perk that lets you walk over traps without setting them off. one of the best parts of the game is keeping an eye out for them and occasionally missing one and having a WTF moment as something big and heavy comes swinging my way.
overall though im very happy with what they have done. i have a blast doing trap only playthroughs where i only kill the mobs with the in dungeon traps and nothing else. bosses are the exception of course.

my favorite aspect is that one a few occasions the npcs actually ran and activated the traps themselves. specifically one time a bandit lady ran down a hallway with me and my follower in tow and she pulle the chain and activated the swinging axes. i was so excited at seeing an npc do that i stopped and proceeded to lose most of my health. it was awesome.